In view of the environmental friendliness, cartridges filled with developer for use in laser printers may be collected after use, refilled with developer, and recycled.
A stopper fitted to a filling port of a cartridge is designed variously to facilitate refilling of developer.
For example, a particular type of the stopper in a thin-walled structure having a bottom portion provided with a knob is known in the art wherein the knob is operative to be pulled out or pushed in so that one can deform the stopper between a high-pressure fitting state and a low-pressure fitting state to thereby smoothly open or close the filling port. Another type of the stopper having an engageable portion is also known in the art wherein a remover jig is engageable with this engageable portion so that the stopper fitted to the filling port can be removed easily.
However, these stoppers are configured to be easy to fit and remove, but their deformable configuration also allows the stoppers to inadvertently come off during transportation or storage.
There is a need to provide a stopper which is easy to fit and less prone to coming off during transportation or storage.